As disclosed in U.S. Pat. No. 8,058,486, the compound 1,1,2,3-tetrachloropropene (HCC-1230xa) is an important precursor that can be used for the production of 2,3,3,3-tetrafluoropropene (HFO-1234yf), which is a low GWP molecule that can be used as an effective refrigerant, fire extinguishing agent, heat transfer medium, propellant, foaming agent, blowing agent, gaseous dielectric agent, sterilant carrier, polymerization medium, particulate removal fluid, carrier fluid, buffing abrasive agent, displacement drying agent and power cycle working fluid, to name but a few.
Methods for making 1,1,2,3-tetrachloropropene (HCC-1230xa) are known. For example, U.S. Pat. No. 4,650,914 provides a multi-step process in which 1,1,1,3-tetrachloropropane is generated, purified, and fed to a dehydrochlorination reactor to produce two trichloropropene isomers, namely 1,1,3- and 3,3,3-trichloropropenes ((HCC-1240za and HCC-1240zf, respectively). As shown below, in steps (4) and (5) of the process, the compound 1,1,2,3-tetrachloropropene (HCC-1230xa) is formed.
The steps are:
(1) preparing 1,1,1,3-tetrachloropropane by reacting ethylene with carbon tetrachloride in the presence of both a source of metallic iron that is effective as an activator for the reaction, and a promoter for the reaction, said promoter being selected from organic phosphite and organic phosphate compounds;
(2) dehydrochlorinating the 1,1,1,3-tetrachloropropane to produce a mixture of 1,1,3- and 3,3,3-trichloropropenes;
(3) chlorinating at least one of the trichloropropenes obtained by the dehydrochlorination step to produce 1,1,1,2,3-pentachloropropane;
(4) dehydrochlorinating the 1,1,1,2,3-pentachloropropane to produce a mixture of 1,1,2,3- and 2,3,3,3-tetrachloropropenes; and
(5) contacting the mixture of tetrachloropropenes with anhydrous ferric chloride acting as an allylic rearrangement catalyst, thereby converting the 2,3,3,3-tetrachloropropene to 1,1,2,3-tetrachloropropene.
In Step 1 of the '914 process, carbon tetrachloride is reacted with ethylene in the presence of iron and a phosphorus (V) compound containing a phosphoryl group, preferably an alkyl phosphate chelating agent (such as tributyl phosphate) to form 1,1,1,3-tetrachloropropane. Next, the 1,1,1,3-tetrachloropropane product is fed to a Step 2 dehydrochlorination reactor that contains a base. The resulting products are subject to phase separation and the organic phase containing 1,1,3-trichloropropene (HCC-1240za) and 3,3,3-trichloropropene (HCC-1240zf) was used directly in the next step.
In Step 3 of the '914 process, the trichloropropene mixture is reacted with chlorine to form 1,1,1,2,3-pentachloropropane (HCC-240db). Next, the HCC-240db product is fed to a Step 4 dehydrochlorination reactor that contains a base to form a mixture of 1,1,2,3- and 2,3,3,3-tetrachloropropenes.
In Step (5) the compound 2,3,3,3-tetrachloropropene (HCC-1230xf) is isomerized to 1,1,2,3-tetrachloropropene (HCC-1230xa) in the presence of a Lewis acid catalyst, particularly ferric chloride.
The present invention provides improvements to this reaction scheme, whereby the desired product 1,1,2,3-tetrachloropropene (HCC-1230xa) is formed with less capital expense.